This invention generally relates to disk drives and other data storage devices. More particularly, this invention relates to disk drives having read/write channels with diagnostic digital to analog converters.
Disk drives are used as data storage components for computer systems and other electronic devices. Disk drives include computer hard disk drives, fixed disk drives, and the like. In general, disk drives have lower costs, higher storage capacities, higher reliability, lower power consumption, higher data transfer speed, and smaller physical size than other data storage devices.
A disk drive usually has one or more rotating magnetic disks encased within a housing. The disk drive includes various components for reading and writing data onto the magnetic disks and for interfacing with other devices. Typically, one or more read/write heads are positioned above the magnetic disks to read and write data. The read/write heads may be positioned on each side of a magnetic disk. The read/write head essentially forms the interface between a magnetic disk and the electronic components of the disk drive.
Each read/write head generates or senses electromagnetic fields or magnetic encodings on the magnetic disk as areas of magnetic flux. The presence or absence of flux reversals in the electromagnetic fields represents the data stored on the magnetic disk. A flux reversal is a change in the magnetic flux on contiguous areas of the magnetic disk. The presence or absence of magnetic flux reversals correspond to binary 1""s and 0""s of a diagnostic input signal. To xe2x80x9cwritexe2x80x9d data onto a magnetic disk, electronic components receive data from a host device and translate the data into magnetic encodings. The head transfers the magnetic encodings onto a portion of the magnetic disk. To xe2x80x9creadxe2x80x9d data from the magnetic disk, the head is positioned adjacent to the portion of the magnetic disk having the desired magnetic encodings. The head senses and transfers the magnetic encodings from the magnetic disk. The electronic components translate the magnetic encodings into the data, which is transferred to the host device. The host device may be a personal computer or other electronic equipment. The electronic components may apply error detection and correction algorithms to ensure accurate storage and retrieval of data from the magnetic disk. To improve data storage densities on disk drives, magneto resistive and inductive read/write heads have been developed with increased sensitivity to sense smaller amplitude magnetic signals and with increased signal discrimination.
Typically, a hard drive reads data by xe2x80x9cpeak detectionxe2x80x9dxe2x80x94detecting a voltage peak created when a flux reversal on a magnetic disk passes underneath the read/write head. However, a partial response maximum likelihood (PRML) algorithm has been developed to improve peak detection as densities and rotational speeds increase. PRML is implemented in the disk drive electronics to interpret the magnetic signals sensed by the read/write heads. PRML disk drives read the analog waveforms generated by the magnetic flux reversals stored on the disk. Rather than look for peak values to indicate flux reversals, PRML digitally samples the analog waveform (the xe2x80x9cpartial responsexe2x80x9d portion of the algorithm) and applies signal processing methodologies to determine the bit pattern represented by the waveform (the xe2x80x9cmaximum likelihoodxe2x80x9d portion of the algorithm).
The electric and mechanical components of the disk drive typically include a spindle motor, an actuator assembly, the read/write heads, amplifiers, a read/write channel, and a controller. There may be additional or different components having other configurations. The spindle motor holds and turns the magnetic disks. The actuator assembly positions the read/write heads adjacent to the magnetic disks. The amplifiers increase the signals between the read/write heads and the read/write channel. The controller interfaces between the read/write channel and the host device.
The read/write channel usually is implemented on an integrated circuit, which may be a complementary metal oxide semiconductor (CMOS). Many hard drives include an additional digital to analog converter (DAC) and an additional analog to digital converter (ADC) for diagnostic testing of the read/write channel. These DAC and ADC are in addition to the other digital to analog converters and analog to digital converters used to perform the reading and writing operations in the read/write channel. Typically, the additional ADC and DAC are used for diagnostic testing when the read/write channel is manufactured. Often after manufacturing, no additional diagnostic testing of the read/write channel is performed using the additional ADC or DAC.
The additional DAC has a resolution of about seven bits and receives input from one or more of the digital components in the read/write channel. The additional DAC provides a DAC output voltage or analog signal corresponding to the performance of the digital components in the read/write channel. The DAC output voltage may be connected to a measurement or display device to determine whether the components in the read/write channel are operating within acceptable parameters. The DAC output voltage may pass through a multiplexer, where the DAC output voltage is processed with one or more output voltage signals from the analog components in the read/write channel. The output voltage signals correspond to the performance of the analog components in the read/write channel. From the multiplexer, the DAC output voltage and the output voltage signals may pass through a pin driver buffer. The pin driver buffer helps distinguish between the output signals and may provide the output signals to the measurement or display device.
The additional ADC receives an input voltage or analog signal from outside or inside the read/write channel. The additional ADC produces a digital output for diagnostic testing of external and internal components. The input voltage may vary, which would change the digital output and thus provide additional testing parameters. The ADC usually operates at a moderate speed and has a resolution of about six to seven bits. The additional ADC usually has a flash or direct conversion, an integrating, a sigma-delta or over sampling, or a pipeline design. These ADC designs increase the hardware requirements and thus the size and costs of the read/write channel.
This invention provides a read/write channel with a diagnostic system for a disk drive. The diagnostic system uses bit-weighing or successive approximation to convert an analog input signal into a digital diagnostic signal.
The disk drive may have a read/write channel and a diagnostic system. The read/write channel may be implemented on an integrated circuit. The diagnostic system may have bit-weighing conversion and a diagnostic output responsive to a diagnostic input voltage. The diagnostic system may include a digital to analog converter, an analog comparator, and a successive approximation register. The digital to analog converter may have an analog output responsive to a diagnostic input signal. The analog comparator may be coupled to compare the diagnostic input voltage with the analog output. The successive approximation register may be coupled to receive at least one register value from the analog comparator, the successive approximation register having the diagnostic output responsive to the at least one register value.
The read/write channel for a disk drive may be implemented on an integrated circuit and may have a digital to analog converter, an analog comparator, and a successive approximation register. The digital to analog converter may be coupled to receive at least one clock signal. The digital to analog converter may have an analog output responsive to a diagnostic input signal and the at least one clock signal. The analog comparator may be coupled to compare a diagnostic input voltage with the analog output from the digital to analog converter. The successive approximation register may be coupled to receive at least one register value from the analog comparator. The successive approximation register may have a diagnostic output responsive to the at least one register value.
The read/write channel for a disk drive may be implemented on a complementary metal oxide semiconductor and may have partial response maximum likelihood (PRML) encoding and decoding. The read/write channel may have a digital multiplexer, one or more clock generators, a digital to analog converter, a first analog multiplexer, a pin driver buffer, an analog comparator, and a successive approximation register. The digital to analog converter may be coupled to receive a diagnostic input signal from the digital multiplexer. The digital to analog converter also may be coupled to receive one or more clock signals from the clock generators. The digital to analog converter may generate an analog output voltage in response to the diagnostic input signal and the clock signals. The first analog multiplexer may be coupled to receive the analog output voltage from the digital to analog converter. The pin driver buffer may be coupled to receive the analog output voltage and one or more test signals from the first analog multiplexer. The analog comparator may be coupled to receive the analog output voltage from the digital to analog converter. The analog comparator may compare the analog output voltage with the diagnostic input voltage. The successive approximation register may be coupled to receive one or more register value from the analog comparator. The successive approximation register may provide a diagnostic output signal in response to the one or more register values. The digital multiplexer may be coupled to receive the diagnostic output signal from the successive approximation register.
Other systems, methods, features, and advantages of the invention will be or will become apparent to one skilled in the art upon examination of the following figures and detailed description. All such additional systems, methods, features, and advantages are intended to be included within this description, within the scope of the invention, and protected by the accompanying claims.